1. Field of the Invention
The present invention relates to a camera having a built-in flash which is provided with CPUs and, more particularly, to an apparatus for providing ON-OFF control over the charging of a main capacitor of a flash unit built in a photographic camera. Such a flash unit is disclosed, for example, in U.S. patent application No. 934,055 now U.S. Pat. No. 4,893,140.
2. Description of the Prior Art
In general, modern photographic cameras are remarkably automated and are provided with a multiplicity of functions. It is common practice to incorporate a plurality of one-chip microcomputers (hereinafter referred to as "CPU" or "CPUs") in a single photographic camera. In the field of built-in flash cameras, it is particularly desirable to minimize the number of parts.
A conventional type of apparatus for controlling the charging of a main capacitor of a flash unit is arranged to detect in two steps the fact that a voltage V developed across the main capacitor has reached the level of a reference voltage. That is to say, when V&gt;V.sub.1, a neon glow lamp is turned on and flash photography is enabled and, when V=V.sub.2 (V.sub.2 &gt;V.sub.1), charging is stopped. After one cycle of flash photography has been completed, the aforesaid operation is again performed.
However, since the voltage V developed across the main capacitor is detected in two steps, it is necessary to incorporate two voltage comparing circuits and therefore the number of parts must be increased.
As the remaining capacity of the batteries drops, the time period taken until the level of the voltage V across the main capacitor reaches the level of a predetermined reference voltage V.sub.2 is excessively extended and therefore the power consumption of a DC/DC converter and other circuits also increases. As a result, the number of flashes is reduced.
There are some instances where, after the stop of charging, photographs are taken at intervals which are equal to or longer than the elapsed time period until the level of the voltage V across the main capacitor reaches the level of the reference voltage V.sub.1 as the result of spontaneous discharge, (hereinafter referred to as "spontaneous-discharge period"). For example, an animal which is moving past a predetermined position at night may need to be automatically detected and photographed. In this case, however, it has been impossible to take flash photographs and therefore built-in flash cameras are not suitable for use in photography under these conditions.